Exhaust gas recirculation system fault detector

Abstract

The method for determining a fault in an exhaust gas recirculation system includes comparing the measured exhaust gas flow of the EGR system to an expected exhaust gas recirculation flow. If the two are not the same the time period that the expected exhaust gas recirculation flow deviates from the measured exhaust gas recirculation flow by a calibrated EGR flow amount is determined. A fault condition in the EGR system is indicated if the duration of the deviation exceeds a predetermined amount of time.

What is claimed: 
     
       1. A method of determining a fault in an EGR system includes the steps of: comparing the measured exhaust gas flow through the EGR system to an expected EGR flow;   determining the period of time that the expected flow of EGR deviates from the measured EGR flow by a calibrated EGR flow amount; and   indicating a fault condition in the EGR system if the duration of the deviation exceeds a predetermined amount of time.   
     
     
       2. A method as recited in claim 1 further comprising the steps of: storing hardware characteristics in a read only memory table.   
     
     
       3. A method as recited in claim 1 including the steps of: providing inputs identifying engine speed, air charge, exhaust gas recirculation actual percentage, barometric pressure, air mass and exhaust temperature;   providing stored look-up tables including engine speed versus an EGR multiplier at various air charges (a first table), engine speed versus INT (a second table), engine speed versus slope (a third table), barometric pressure versus a multiplier (a fourth table) and air mass versus PEXHSTP (a fifth table) where PEXHSTP is the exhaust pressure at 29.92 barometric pressure and 1000 Deg. F. exhaust temperature;   applying inputs indicating engine speed to said first table, said second table and said third table;   applying an input indicating air charge to said first table;   applying an input indicating barometric pressure to said fourth table;   applying air mass to said fifth table;   applying the output from said first table and an input indicating exact actual exhaust gas circulation to a first multiplier;   applying the output of said third table to a second multiplier and applying the input indicating air charge to said second multiplier;   applying the output from said first multiplier, said second multiplier and said second table to a first summer;   applying the output of the first summer to the negative input of a second summer and applying the input indicating barometric pressure to a positive input of said second summer;   applying the outputs of said fourth and fifth tables to a third multiplier and applying the input indicating exhaust temperature to said third multiplier;   applying the outputs of said second summer and said third multiplier to a third summer applying the output of said third summer to a sixth table relating system delta pressure to DCSTO; and   providing a DCSTO output from said sixth table and a system delta pressure output from said third summer where DCSTO is the EGR duty cycle EGRDC required overcome the spring force which keeps the EGR valve closed on its seat, versus the pressure drop across the EGR seat which is SYS --  DELPR.   
     
     
       4. A method as recited in claim 1 including the steps of checking for a restricted or plugged exhaust gas recirculation valve including: comparing EGR DC, to V --  EGRDC --  MAX,   if it is not greater, exiting and setting EGR --  VLVPLG--FAULT --  COUNTER, equal to zero;   if it is greater, checking to see if a VAC --  RNG --  FLG is equal to one; if not, then exiting and setting EGR --  VLVPLG --  FAULT --  COUNTER equal to zero; if yes then checking to see if ENG --  STDY --  FLG is equal to one;   if no then exiting and setting EGR --  VLVPLG --  FAULT --  COUNTER equal to zero; if yes setting DELP --  MIN --  VLVPLG; equal to a function of SYS --  DELPR, DC --  VLVPLG, DCSTO;   comparing DELPR to DELPR --  MIN --  VLVPLG if DELPR is less, setting EGR --  VLVPLG --  FAULT --  COUNTER equal to the previous EGR --  VLVPLG --  FAULT --  COUNTER plus an additional step; and if not less setting EGR --  VLVPLG --  FAULT --  COUNTER equal to the previous EGR --  VLVPLG --  FAULT --  COUNTER less one.   
     
     
       5. A method as recited in claim 1 further comprising checking for an EGR valve stuck in the open position including the steps of: checking to see if EGREN is equal to one;   if not, setting EGR --  VLVOPN --  FAULT --  COUNTER equal to zero and exiting; if yes, checking to see if EGRDC is less than EGRDC --  LIM --  VO;   if not, setting the EGR --  VLVOPN --  FAULT --  COUNTER equal to zero and exiting; if yes, checking to see if a VAC --  RNG --  FLG is set equal to zero;   if not, setting the EGR --  VLVOPN --  FAULT --  COUNTER equal to zero and exiting; if yes checking to see if the ENG --  STDY --  FLG is set equal to one;   if not, setting the EGR --  VLVOPN --  FAULT --  COUNTER equal to zero and exiting; if yes, comparing DELPR with respect to DELPR --  MAX --  VLVOPN if DELPR is greater, then EGR --  VLVOPN --  FAULT --  COUNTER counter is equal to the previous plus a step; and if not, then EGR --  VLVOPN --  FAULT --  COUNTER is equal to the previous less one and exiting.   
     
     
       6. A method as recited in claim 1 further comprising checking for restricted EGR metering orifice via high delta pressure including the steps of: checking to see if EGRDC is less than EGRDC --  LM --  ROU;   if no, setting ENG --  RESORF --  FAULT --  COUNTER equal to zero; if yes, checking to see if EGRDC is greater than EGRDC --  LM --  ROL;   if no, setting EGR --  RESORF --  FAULT --  COUNTER equal to zero; if yes, checking to see if VAC --  RNG --  FLG equal to one;   if no, setting the EGR --  RESORF --  FAULT --  COUNTER equal to zero; if yes, checking to see if the ENG --  STDY --  FLG equal to one;   if no, setting the EGR --  RESORF --  FAULT --  COUNTER equal to zero; if yes, checking to see if the EGR --  STDY --  FLG is equal to one;   if no, setting the EGR --  RESORF --  FAULT --  COUNTER equal to zero; if yes, setting DELPR --  MAX --  RESORF equal to a function of the SYS --  DELPR and the DC --  RESORF--DCSTO;   checking to see if DELPR is greater than DELPR --  MAX --  RESORF; if yes, setting the EGR --  RESORF --  FAULT --  COUNTER equal to EGR --  RESORF --  FAULT --  COUNTER plus the EGR --  RESORF --  FAULT --  UP --  STEP; and if no, setting the EGR --  RESORF --  FAULT --  COUNTER equal to EGR --  RESORF --  FAULT --  COUNTER minus one.   
     
     
       7. A method as recited in claim 1 for including the steps of checking for restricted orifice via unstable oscillations including the steps of: checking to see if the EGREN is equal to zero;   if no, setting EGR --  UNSTAB --  FAULT --  COUNTER equal to zero; if yes, checking to see if EGR --  STDY --  FLG is equal to one;   if no, setting EGR --  UNSTAB --  FAULT --  COUNTER equal to zero; if yes, comparing the difference between EGRDC --  LAST and EGRDL to EGRDL --  LIM --  VU;   if the first is not greater than the second, decrementing exhaust gas recirculation fault countered by one;   if the first is greater than the second, comparing the difference between EGRDG --  LAST and EGRDC to EGRDC --  LIM --  VU;   if the first is not greater than the second, decrementing EGR --  UNSTAB --  FAULT --  COUNTER by one; and   if the first is greater than the second, setting EGR --  UNSTAB --  FAULT --  COUNTER equal to the previous EGR --  UNSTAB --  FAULT --  COUNTER plus a step.   
     
     
       8. A method of determining and following operation of an EGR system including the steps of: determining EGR flow is between an upper and a lower limit of EGR flow magnitude;   checking for the disconnection of a downstream hose;   checking for disconnection of an upstream hose;   checking for a restricted or plugged EGR valve;   checking for an EGR valve stuck in an open position;   checking for a restricted EGR metering orifice via a delta pressure; and   checking for a restricted EGR metering orifice via oscillations in an EGR duty cycle.   
     
     
       9. Method as recited in claim 8 wherein the steps of checking for the downstream hose is connected includes: checking to see if EGREN equals one;   if no, setting EGR --  DNHOSE --  FAULT --  COUNTER equal to zero; if yes, checking to see if DELPR is greater than DELPR --  THRES1;   if no, decrementing the EGR --  DNHOSE --  FAULT --  COUNTER; if yes, checking to see if DELPR is greater than the PEXH+EGRDELPR --  TOL;   if no, decrementing the EGR --  DNHOSE --  FAULT --  COUNTER; if yes, checking to see if DELPR is greater than PEXH-EGRDELPR --  TOL;   if no, decrementing the DNHOSE --  FAULT --  COUNTER; and if yes, incrementing the EGR --  DNHOSE --  FAULT --  COUNTER.   
     
     
       10. A method recited in claim 9 wherein the step of checking for upstream hose disconnection includes: checking to see if EGRN is equal to one;   if no, setting the EGR --  UPHOSE --  FAULT --  COUNTER equal to one; if yes, checking to see if DELPR is less than DELPR --  THRES2;   if no, decrementing the EGR --  UPHOSE --  FAULT --  COUNTER; if yes, checking to see if the DELPR is greater than PEXH+EGRDELPR --  TOL;   if no, decrementing the EGR --  UPHOSE --  FAULT --  COUNTER; if yes, checking to see if DELPR is less than PEXH-EGRDELPR --  TOL;   if no, decrementing the EGR --  UPHOSE --  FAULT --  COUNTER; and if yes, incrementing the UPHOSE --  FAULT --  COUNTER.